Some claim that it means just "off" in some way of american speaking
Some say it even means "because" in some cases.
Some say it is a definitely wrong use of grammar.
It’s a way of profiting off of something you expect to drop in value.
Where the "chip" is referring to the son (or sometimes daughter), and the "block" is referring to the father (but seldom the mother). Meaning that the offspring heavily resemble their own parents. Also meaning that the son has acquired a characteristic from their father.
Hey Johnny, that's exactly what your Pop said! You're a real chip off of the old block, ya know that?